This invention relates to fuel cells, and in one embodiment, to fuel cells that are especially well suited for downhole use in oil and gas wells, and for subsea use in connection with offshore wells. The invention can also be useful for commercial energy generation, powering electric vehicles, and powering other equipment, for example, communication and control equipment located in remote areas away from commercially available power sources.
Several types of equipment used downhole in oil and gas wells, or beneath the surface of the sea adjacent to offshore wells, are electrically operated or actuated. Examples of such equipment include certain wireline tools and remote well telemetry equipment. The electrical power required can be provided by connecting the device to a surface power source via electrical cables, or by placing a power source near the site of the device itself. Often it is not practical to use electrical cables running from the surface to the subterranean or subsea site of the electrically-powered device, because of the great distance involved, or because the cables can interfere with the passage of other equipment through the wellbore, and are vulnerable to being damaged during well operations.
Batteries can be used as a local source of power for downhole and subsea electrical devices, but are subject to their own problems. For example, increasing the power and energy generation capacity of a battery generally requires a proportionate increase in the size of the battery, which can present difficulties given the space constraints that exist in wellbores. Also, batteries will typically need to be electrically recharged at some point, thereby often making it necessary to provide some type of recharging equipment in physical proximity to the battery.
Fuel cells make use of an electrochemical reaction involving a fuel and an oxidant in a cell that comprises an anode, cathode, and electrolyte, to generate electricity without also generating the unwanted by-products associated with combustion, while providing relatively higher energy efficiency. Thus, fuel cells potentially have a number of advantages over other power generation or storage means in many applications. The fuel cells of the present invention can be used in a variety of applications. Although the invention is primarily described herein in relation to applications involving subterranean wellbores, it should be understood that the invention can be used in applications other than wellbore applications.
A number of obstacles have hindered the use of fuel cells in downhole and subsea applications. For instance, fuel cells typically include one or more pumps to provide circulation of fuel and/or oxidant in a closed loop through the cell. If such a pump fails downhole, repair or replacement can be extremely expensive, given the need to retrieve the fuel cell to the surface. Further, the operation of the pumps consumes some of the energy produced by the cell, thus reducing the net power yield available to operate an external device. This latter point can be a significant problem in downhole or subsea applications in which a supply of power is needed for an extended period of time, and yet space constraints limit the ability to simply increase the size of the fuel and oxidant reservoirs. Additionally, the reaction product, water vapor, needs to be removed from the fuel cell stack in order to continuously run the fuel cell. Removal of the water downhole and in a subsea environment presents a challenge because the surrounding pressure is higher than that present in a conventional fuel cell placed at surface in an ambient environment and operating in air. Using a pump to expel the water into the high pressure downhole or subsea environment may require a large amount of power making such a system impractical.
VanBerg U.S. Pat. No. 5,202,194 describes a power supply for providing electricity to electrical circuits located downhole in a well. The power supply comprises a fuel cell, which is fed by hydrogen from a pressure container and oxygen from compressed oxygen gas bottles. Pressure regulators are located in the line between the hydrogen container and the fuel cell, and in the line between the oxygen bottles and the fuel cell. A pump is used to eject water from the fuel cell into the wellbore. The need to have a water outflow path from the interior of this fuel cell to its exterior raises potential reliability issues and may be impractical for downhole use.
There is a need for a new fuel cell operation concept and an improved fuel cell apparatus that can provide the electrical power needed to operate various downhole and subsea equipment.
One embodiment of the present invention relates to a fuel cell that includes a fuel vessel that comprises a source of fuel and an oxidant vessel comprising a source of oxidant. A reaction zone comprises at least one cathode, at least one anode, and electrolyte between each anode and cathode. A closed water vessel is connected to the reaction zone by at least one capillary flow path. The fuel cell also comprises a fuel conduit that connects the fuel vessel and the reaction zone. This fuel conduit comprises a fuel pressure control apparatus adapted to maintain a static pressure of fuel in the reaction zone. The fuel cell further comprises an oxidant conduit that connects the oxidant vessel and the reaction zone, and includes an oxidant pressure control apparatus adapted to maintain a static pressure of oxidant in the reaction zone. In addition, the fuel cell comprises electrical conductors connected to the anode and cathode and adapted to conduct electricity to an external device.
In a fuel cell of certain embodiments of the present invention, there is no need for fuel, oxidant, or water to dynamically flow in a closed loop through the reaction zone. This is because the fuel and oxidant vessels, and the pressure control apparatus, provide a static, elevated pressure in the reaction zone. The closed water vessel receives and stores the water (liquid) produced by the fuel cell reaction, thus eliminating the need to pump the water out of the fuel cell for disposal.
In some embodiments, the fuel cell of the present invention does not include any fuel pump, oxidant pump, or water pump. As mentioned above, such pumps are not required in some embodiments of the present invention. It is also possible that the reaction zone comprise as its only openings for fluid flow at least one aperture connected to the fuel conduit for admitting fuel into the reaction zone, at least one aperture connected to the oxidant conduit for admitting oxidant into the reaction zone, and the capillary flow path (or paths) that connects the reaction zone to the water vessel. The capillary flow path can comprise a tube, thread, conduit or other forms that can transport the produced water from the reaction zone to the water vessel and can be attached to or lying on or otherwise physically touching the membrane surfaces of the reaction zone.
The fuel cell of some embodiments of the present invention is operated with a static pressure in the reaction zone that is high enough to cause any water vapor formed and generated in the fuel cell to condense once the saturation point is reached. Accordingly, the fuel cell must operate at a pressure that is higher than the saturated water vapor pressure for the given application. A xe2x80x9cstatic pressurexe2x80x9d in this context is one that varies between the anode and cathode chamber of the fuel cell not more than about 5% in normal operation. Some embodiments of the invention operate with pressures for the reaction zone between about 40-400 psig, more typically about 50-200 psig, depending upon the operating temperature.
In one specific embodiment of the invention, the fuel pressure control apparatus and the oxidant pressure control apparatus are pressure regulator valves. In another specific embodiment of the invention, the water vessel is located within at least one cathode. In other embodiments the water vessel is located external to the reaction zone.
Although the fuel cell of the present invention can operate with a single anode, cathode, and electrolyte, in many applications it will be desirable to have multiple cells in a single apparatus. Therefore, an alternate embodiment comprises at least one additional fuel cell that includes an anode, cathode, and electrolyte, with the fuel cells being arranged in a stack configuration. In this embodiment of the invention, at least one bipolar plate that comprises the anode of one fuel cell in the stack and the cathode of an adjacent fuel cell in the stack can be included. For example, the bipolar plate can comprise two substantially planar surfaces, the anode being located on one of the surfaces and the cathode being located on the other surface. xe2x80x9cSubstantially planarxe2x80x9d in this context means that the overall surface of the plate is generally planar, although there may be grooves in the surface to facilitate distribution of fuel or oxidant.
The present invention can be used with a variety of types of fuel cells, including phosphoric acid fuel cells and alkaline fuel cells.
The present invention is especially well adapted for use with proton exchange membrane fuel cells. Embodiments of the invention can operate at an elevated temperature and pressure. The temperature can operate, for example, within the range of 80xc2x0 C. to 130xc2x0 C. The higher operating pressure (up to 400 psi) keeps the membrane from dehydrating at the elevated operating temperature (more than about 80xc2x0 C.). The pressure regulators on the fuel and oxidant supplies control the operating pressure. The temperature and pressure controls allow a balance to be met that allows the membrane to stay hydrated while also enabling the condensation of the water vapor and the liquid water removal from the reaction zone. The closed end nature of the fuel cell, wherein the fuel and oxidant supply each have an inlet to the reaction zone but there is no gas outlet from the reaction zone, allows the operation at elevated pressures. The only outlet from the reaction zone is the outlet to remove produced water. If produced water is not removed from the reaction zone the water will build up and the fuel cell would not be able to continue the reaction. If the membrane were to become dehydrated, the fuel cell would fail because the membrane must be wet to operate. In a particular embodiment of the proton exchange membrane fuel cell, the electrolyte between the anode and cathode comprises a polymer material.
The present invention is also well adapted for use with solid oxide fuel cells. The higher operating temperatures, such as 700 degrees C., of a solid oxide fuel cell enables the use of this type cell in even the most extreme high temperature well applications. In a solid oxide fuel cell, water is produced on the anode side, so the water vessel is in communication with the anode. The water vessel can comprise a metal hydride material that is capable of reacting with the water byproduct of the fuel cell and releasing hydrogen gas. This produced hydrogen gas can be utilized as fuel and can be transported from the water vessel to the fuel conduit by means of a fuel recycle conduit. A fuel regeneration vessel can be connected to the anode portion of the reaction zone by one or more flow paths that can enable it to receive produced water. The metal hydride material contained in the fuel regeneration vessel can react with the water and produce hydrogen gas. A regenerated fuel conduit connecting the fuel regeneration vessel to the fuel conduit transports the hydrogen gas. An internal pump can be included with the regeneration vessel or the regenerated fuel conduit to enable the gas to combine with the fresh fuel. In a solid oxide fuel cell the electrolyte will typically comprise a solid ceramic material.
A further embodiment of the present invention comprises a housing and at least one membrane within the housing, the membrane having opposing surfaces. A supply of oxygen is in communication with one surface of the membrane while a supply of hydrogen is in communication with the other surface of the membrane. The membrane comprises at least one slanted surface. The membrane can have a shape, for example, such as frustoconical, conical, hemispherical, bowl-shaped, or curved. As with some of the other embodiments, it is possible for this fuel cell to comprise no internal moving parts and can be connected to a battery to form a hybrid power supply.
Yet another embodiment is a fuel cell as described above which also comprises at least one separator/electrode plate adjacent to the membrane. The separator/electrode plate is constructed so as to define at least one groove, the groove having a coating of a hydrophobic material such as wax or grease. The hydrophobic material facilitates the removal of produced water from the reaction zone.
Another embodiment comprises at least one reservoir that is in fluid communication with an area proximal to at least one of the surfaces on the membrane. The reservoir may be positioned below the membrane, so gravitational forces can assist in the water removal. The reservoir can be positioned to receive produced water in the form of steam or liquid and can further comprise a screen intermediate in the inlet and the outlet, a desiccant within the reservoir, and a water chamber. The fuel cell can also comprise a pump communicating with a reservoir outlet and can comprise an internal circulation pump communicating with the fresh oxidant inlet.
The fuel vessel and oxidant vessel can take different forms in the present invention. For example, the fuel vessel can comprise a pressure vessel that holds pressurized hydrogen gas or reformed hydrocarbon gas. However, alternate embodiments of the invention can include a fuel vessel comprising at least one metal hydride capable of releasing hydrogen gas. The use of metal hydride as a storage means for hydrogen provides a very efficient use of space, which can be an important consideration in downhole and subsea applications. Also, the metal hydride hydrogen storage improves the safety of the fuel cell by allowing operation at lower pressures relative to the pressures required if pure hydrogen were used. It should be noted that, while the present invention is described with operating ranges, different types of metal hydride are available that operate at higher pressures, such as between 500 and 800 psi, for example. Using these higher pressure metal hydrides can increase the operating temperature of the fuel cell to 100xc2x0 C. to 200xc2x0 C. or higher. The oxidant vessel can comprise, for example, a pressure vessel that contains oxygen gas at a pressure of at least about 1,000 psig, or alternately at least about 5,000 psig, to about 15,000 psig.
Fuel cells of the present invention are very well suited for applications in which a low power output is needed for an extended time. For example, in one embodiment of the invention, the fuel cell has a power output of at least about 1 watt (e.g., 1-30 watts, often about 10-20 watts) for a period of several weeks. Larger fuel cell apparatus of the present invention can also be used in applications requiring higher power output. In some alternate embodiments in higher power applications the oxygen may be circulated, which can facilitate a higher power output.
In one embodiment of the invention, the fuel cell further comprises a housing that encloses at least part of the reaction zone and comprises a cylindrical outer wall. In other words, the housing encloses part or all of the reaction zone, and optionally can also enclose the fuel and oxidant vessels. The housing may also comprise a cylindrical inner wall that defines an open longitudinal bore in the fuel cell. In this embodiment of the invention, the annular configuration of the fuel cell makes it well suited for use downhole in oil and gas wells by defining at least one passageway through the fuel cell. Passageways within the fuel cell can be useful through which to produce formation fluids or to run cables, conduits or other devices. The housing may alternatively comprise a portion of an annulus or some other shape that facilitates placement in an annular space. Circular or cylindrical devices are also particularly useful for downhole applications. The housing can enclose the produced water vessel in addition to the fuel and oxidant vessels and the reaction zone. In one embodiment of the invention, the housing encloses the entire fuel cell, except for the electrical conductors that are adapted to conduct electricity to an external device.
The purpose of placing the fuel cell downhole in a well, or in a subsea location in or adjacent to an offshore well, is to supply power to an electrical device. Therefore, in such applications, the apparatus may also comprise a downhole electrical device, or a subsea electrical device, which is electrically connected to the fuel cell (e.g., by wires or electrical cables). In some embodiments of the invention the fuel cell is connected to a battery to form a hybrid power source. The battery can be of a rechargeable type that can be charged from the fuel cell during less than peak power demand and can discharge in order to assist the fuel cell during peak power demand. The battery-fuel cell hybrid power source can thus supply a broader range of power loads than the fuel cell acting alone can supply.
One particular embodiment of the present invention is a power supply system that comprises a fuel cell and a rechargeable battery that is electrically connected to the fuel cell such that the fuel cell recharges the rechargeable battery during periods of non-use.
Another aspect of the present invention is a downhole assembly that comprises a downhole structure (e.g., a drillstring, well casing, or well tubing) located in a subterranean borehole. A fuel cell, as described above, is attached to the downhole structure and a downhole electrical device is electrically connected to the fuel cell. Yet another aspect of the present invention is a subsea assembly that comprises a subsea structure (e.g., a riser pipe), for an offshore well and a fuel cell (as described above) attached to the subsea structure. A subsea electrical device (e.g., an umbilical-less control system) is electrically connected to the fuel cell.
The present invention provides a simple, reliable, and efficient means of generating electrical power in a downhole or subsea environment. The fuel cell apparatus of the present invention can provide power without the need for any moving parts, thereby decreasing the chance of a mechanical failure.
The fuel cell apparatus of the present invention is also useful for remote power applications, such as providing power for geosensors located at the surface of the earth in locations spaced far enough apart that installing and replacing conventional batteries would be burdensome and expensive.
The present invention also has safety benefits. The embodiments of the present invention that use metal hydride as a means for storing hydrogen largely eliminate the safety risks involved with storing hydrogen gas under high pressure.
The closed nature of the fuel cell apparatus of certain embodiments of the present invention provides improved reliability compared to prior fuel cells. Since no fluid of any kind needs to be pumped from the inside of the fuel cell apparatus to an external location, there are no apertures to the outside world that could become a source of leaks, and there is no need for a pump that would consume part of the power generated by the fuel cell and could potentially break down.
The static elevated pressure operation of the present invention keeps the membrane in a proton exchange membrane fuel cell hydrated, and thus allows operation at a wide range of temperatures (e.g., 0-150xc2x0 C.).
The power generation capacity of fuel cells can be increased simply by using a higher capacity fuel vessel and/or a larger capacity oxidant vessel. Thus, unlike batteries, an increase in the power and energy generation capacity of a fuel cell does not require a proportional increase in its size.
One embodiment of the present invention is a method for supplying power to a well comprising providing a fuel cell within or near the well. The method can comprise electrically connecting the fuel cell to a downhole electrical device and connecting a battery to the fuel cell to form a hybrid power source. The method can also comprise connecting the fuel cell to a tubular string and inserting the fuel cell and tubular string into the wellbore.
Yet another embodiment is a method for completing a wellbore by providing a fuel cell comprising a fuel vessel for a source of fuel and an oxidant vessel for a source of oxidant. The fuel cell has a reaction zone having at least one cathode, at least one anode, and electrolyte between each anode and cathode. A closed water vessel is connected to the reaction zone by at least one capillary flow path. A fuel conduit connects the fuel vessel and the reaction zone, and comprises a fuel pressure control apparatus adapted to maintain a static pressure of fuel in the reaction zone. An oxidant conduit connects the oxidant vessel and the reaction zone and comprises an oxidant pressure control apparatus adapted to maintain a static pressure of oxidant in the reaction zone. Electrical conductors are connected to the anode and cathode and adapted to conduct electricity to an external device. The fuel cell is connected to an electrical device and the fuel cell and electrical device are inserted into the wellbore. The fuel cell can be connected to a battery, thus forming a hybrid power source. The fuel cell can be constructed to define at least one passageway through the fuel cell. Formation fluids may then be produced from the wellbore, the formation fluids flowing through the passageway defined by the fuel cell.
Still another embodiment is a method of supplying power to an electrical circuit of a downhole tool that comprises providing a fuel cell comprising a housing, a fuel vessel, an oxidant vessel and electrical connectors, where the fuel cell is enclosed within the housing except for the electrical connectors. The fuel cell is electrically connected to the electrical circuit of the downhole tool and the downhole tool and fuel cell are inserted into a wellbore. Electricity is generated within the wellbore from the fuel cell and supplies at least some of the electricity needed to energize the electrical circuit of the downhole tool. A battery may be electrically connected to the fuel cell, thus forming a hybrid power supply capable of storing a portion of the electricity generated by the fuel cell. The fuel cell can further comprise a pump and an outlet, the pump being capable of discharging produced water from the outlet of the fuel cell. An alternate embodiment of this method utilizes a fuel cell that comprises no internal moving parts. Water produced within the fuel cell can be contacted with metal hydride material to produce hydrogen gas, which can be injected into a fuel supply line to the fuel cell reaction zone.
Another alternate embodiment is a fuel cell comprising a proton exchange membrane, a closed end chamber on an oxygen side of the membrane and a closed end chamber on a hydrogen side of the membrane. A water vessel may be connected to at least one of the closed end chambers by at least one capillary flow path in which to store the water byproduct produced. The fuel cell can further comprise a proton exchange membrane, a pressurized oxygen supply communicating with a first side of the membrane, and a pressurized hydrogen supply communicating with a second side of the membrane. The pressurized supply of oxygen and hydrogen are capable of maintained the first and second membranes within a pressure range of about 30 to 300 psi.
A method for use with a fuel cell comprises providing a proton exchange membrane fuel cell and operating the fuel cell at a temperature equal to or greater than 90xc2x0 C. In some embodiments the operating temperature can be equal to or greater than 100xc2x0 C., or alternately equal to or greater than 120xc2x0 C.
Another embodiment of the invention is a method for use with a fuel cell comprising providing a proton exchange membrane fuel cell that generates water vapor during operation, and condensing a portion of the water vapor within the fuel cell. The condensing of the water can occur within the reaction zone and some of the liquid water can be removed from the reaction zone by a capillary flow path to a water vessel.
Certain embodiments of the present invention can be applied as a power source for use in a well, comprising a proton exchange membrane-type fuel cell, and as a method for powering a tool in a well, comprising operatively connecting a proton exchange-type fuel cell to the tool.
Certain embodiments of the present invention can also be applied as a power source for use in a well, comprising a solid oxide-type fuel cell, and as a method for powering a tool in a well, comprising operatively connecting a solid oxide-type fuel cell to the tool.
An alternate embodiment of the invention is as a method for providing power in a high temperature well, comprising providing a fuel cell capable of operating temperatures at or above 600xc2x0 C. This fuel cell can operate in environments with temperatures from 0xc2x0 C. to 1,000xc2x0 C.
Still another embodiment is a fuel cell comprising at least one capillary member, which can have at least one membrane/electrode assembly and at least one water vessel. The at least one capillary member is capable of transporting water from the membrane/electrode assembly to the water vessel. One end of the at least one capillary member is located on the surface of the membrane/electrode assembly, extending away from the surface of the membrane/electrode assembly while the other end of the capillary member is in contact with the water vessel. The at least one capillary member is capable of communicating water from the membrane/electrode surface to the water vessel. More than one capillary member can communicate water from the membrane/electrode surface to a common water vessel.